Structural insights into a novel nonheme iron-dependent oxygenase in selenoneine biosynthesis.

Selenoneine (SEN) is a natural histidine derivative with radical-scavenging activity and shows higher antioxidant potential than its sulfur-containing isolog ergothioneine (EGT). Recently, the SEN biosynthetic pathway in Variovorax paradoxus was reported. Resembling EGT biosynthesis, the committed step of SEN synthesis is catalyzed by a nonheme Fe-dependent oxygenase termed SenA. This enzyme catalyzes oxidative carbon­selenium (C-Se) bond formation to conjugate N-α-trimethyl histidine (TMH) and selenosugar to yield selenoxide; the process parallels the EGT biosynthetic route, in which sulfoxide synthases known as EgtB members catalyze the conjugation of TMH and cysteine or γ-glutamylcysteine to afford sulfoxides. Here, we report the crystal structures of SenA and its complex with TMH and thioglucose (SGlc), an analog of selenoglucose (SeGlc) at high resolution. The overall structure of SenA adopts the archetypical fold of EgtB, which comprises a DinB-like domain and an FGE-like domain. While the TMH-binding site is highly conserved to that of EgtB, a various substrate-enzyme interaction network in the selenosugar-binding site of SenA features a number of water-mediated hydrogen bonds. The obtained structural information is beneficial for understanding the mechanism of SenA-mediated C-Se bond formation.

Remodeling the polymer-binding cavity to improve the efficacy of PBAT-degrading enzyme.

Poly(butylene adipate-co-terephthalate) (PBAT) is among the most widely applied synthetic polyesters that are utilized in the packaging and agricultural industries, but the accumulation of PBAT wastes has posed a great burden to ecosystems. Using renewable enzymes to decompose PBAT is an eco-friendly solution to tackle this problem. Recently, we demonstrated that cutinase is the most effective PBAT-degrading enzyme and that an engineered cutinase termed TfCut-DM could completely decompose PBAT film to terephthalate (TPA). Here, we report crystal structures of a variant of leaf compost cutinase in complex with soluble fragments of PBAT, including BTa and TaBTa. In the TaBTa complex, one TPA moiety was located at a polymer-binding site distal to the catalytic center that has never been experimentally validated. Intriguingly, the composition of the distal TPA-binding site shows higher diversity relative to the one proximal to the catalytic center in various cutinases. We thus modified the distal TPA-binding site of TfCut-DM and obtained variants that exhibit higher activity. Notably, the time needed to completely degrade the PBAT film to TPA was shortened to within 24 h by TfCut-DM Q132Y (5813 mol per mol protein). Taken together, the structural information regarding the substrate-binding behavior of PBAT-degrading enzymes could be useful guidance for direct enzyme engineering.

Griseofamines A and B: Two Indole-Tetramic Acid Alkaloids with 6/5/6/5 and 6/5/7/5 Ring Systems from Penicillium griseofulvum.

Two novel indole-tetramic acid alkaloids-griseofamine A (1) and griseofamine B (2)-and ( R)- N-(2-methylbutanoyl)-l-tryptophan (3), were isolated from the fungus Penicillium griseofulvum. Compounds 1 and 2 feature a 6/5/6/5 and 6/5/7/5 tetracyclic ring systems formed by the fusion of an indole unit and a tetramic acid via a six or seven-membered N-heterocyclic ring, respectively. The plausible biosynthetic pathways of 1-3 are proposed. Compound 1 shows a weak anti-inflammatory activity by inhibition of NO and TNF-α production.